OP0116 THE AP-1 TRANSCRIPTION FACTOR FOSL-2 DRIVES CARDIAC FIBROSIS AND ARRHYTHMIAS UNDER IMMUNOFIBROTIC CONDITIONS IN SYSTEMIC SCLEROSIS
Authors: M. Stellato, M. Dewenter, M. Rudnik, A. Hukara, O. Cagla, F. Renoux, E. Pachera, F. Gantenbein, P. Seebeck, S. Uhtjaerv, E. Osto, D. Razansky, K. Klingel, J. Henes, O. Distler, P. Błyszczuk, G. Kania
Journal: Annals of the Rheumatic Diseases (2023)

<h3>Background</h3> Fibrotic changes in the myocardium and cardiac arrhythmias represent fatal complications in systemic sclerosis (SSc). So far, the underlying mechanisms remain elusive. Mice overexpressing AP-1 family transcription factor Fosl-2 (Fosl-2<sup>tg</sup>) represent animal model of SSc. <h3>Objectives</h3> We aimed to identify the mechanisms controlling myocardial fibrosis and arrhythmias in SSc. <h3>Methods</h3> Mice overexpressing activator protein-1 transcription factor component Fos-related antigen-2 (Fosl-2<sup>tg</sup>) and Rag2<sup>-/-</sup>Fosl-2<sup>tg</sup> mice lacking T and B cells were subjected to study myocardial fibrosis, arrhythmias and response to stress using radiotelemetry, echocardiography and ex-vivo Langendorff-system. Immunohistochemistry/immunofluorescence analyses were used to characterized endomyocardial biopsies (EMBs) of SSc patients with heart failure with or without arrhythmia, and mouse hearts. Cardiac human and mouse fibroblasts were used to evaluate molecular mechanisms using bulk RNA sequencing, qPCR, IF, ELISA, Western blot, Bromodeoxyuridine proliferation assay, senescence associated-β-Galactosidase assay for cell senescence, Caspase Glo 3/7 assay for cell apoptosis and contraction assay. <h3>Results</h3> Fosl-2<sup>tg</sup> mice showed interstitial cardiac fibrosis with increased numbers of CD45<sup>-</sup>CD31<sup>-</sup>Ter119<sup>-</sup>gp38<sup>+</sup> cardiac fibroblasts, disorganized connexin 43 and 40 in intercalated discs and deregulated expression of genes controlling conduction system (<i>Meis1, Nfia</i>, <i>Tbx3</i>, <i>Sox5</i>, <i>Scn10a</i>, <i>Kcnq1</i>, <i>Scn10a, Nos1ap</i>). Fosl-2<sup>tg</sup> mice developed higher heart rate (HR), prolonged QT intervals, arrhythmias with prevalence of premature ventricular contractions, ventricular tachycardias and atrio-ventricular blocks second-degree. QT intervals positively correlated with AV blocks, while QT intervals and AV blocks positively correlated with the disease phenotype and collagen deposition. Fosl-2<sup>tg</sup> mice showed significantly reduced HR variability in long-term ECG recordings (reduced NN intervals, SDNN, RMSSD, NN6, pNN6), indicating autonomic disbalance with a shift towards increased sympathetic activity. Following stimulation with isoproterenol (ISO) Fosl-2<sup>tg</sup> mice revealed impaired HR response. Similarly, ex vivo Langendorff-system measurement of HR in the isolated mouse hearts confirmed the abrogated response to ISO stimulation of Fosl-2<sup>tg</sup> hearts. Immunodeficient Rag2<sup>-/-</sup>Fosl-2<sup>tg</sup> mice showed no myocardial fibrosis and ECG abnormalities. Transcriptomics analysis of cardiac Rag-2<sup>-/-</sup>Fosl-2<sup>wt</sup>/Rag2<sup>-/-</sup>Fosl-2<sup>tg</sup>/Fosl-2<sup>tg</sup> fibroblasts revealed that systemic inflammation triggered fibrotic and arrhythmogenic alterations while Fosl-2-overexpression mediated profibrotic signature. In human cardiac fibroblasts FOSL-2-overexpression enhanced myofibroblast signature under proinflammatory or profibrotic stimuli. Furthermore, increased numbers of GP38<sup>+</sup> fibroblasts were detected in FOSL-2-expressing and collagen-rich areas of SSc EMBs. <h3>Conclusion</h3> These results demonstrate that under inflammatory and fibrotic conditions Fosl-2 drives myocardial fibrosis, arrhythmias and causes aberrant response to stress. This mechanism might represent a promising target against increased cardiac disease burden in the immunofibrotic cardiac disorders. <h3>REFERENCES:</h3> NIL. <h3>Acknowledgements:</h3> NIL. <h3>Disclosure of Interests</h3> Mara Stellato: None declared, Matthias Dewenter: None declared, Michal Rudnik: None declared, Amela Hukara: None declared, Ozsoy Cagla: None declared, Florian Renoux: None declared, Elena Pachera: None declared, Felix Gantenbein: None declared, Petra Seebeck: None declared, Siim Uhtjaerv: None declared, Elena Osto: None declared, Daniel Razansky: None declared, Karin Klingel: None declared, Jörg Henes: None declared, Oliver Distler Consultant of: OD has/had consultancy relationship with and/or has received research funding from or has served as a speaker for the following companies in the area of potential treatments for systemic sclerosis and its complications in the last three years: Abbvie, Acceleron, Alcimed, Amgen, AnaMar, Arxx, AstraZeneca, Baecon, Blade, Bayer, Boehringer Ingelheim, Corbus, CSL Behring, Galapagos, Glenmark, Horizon, Inventiva, Kymera, Lupin, Medscape, Miltenyi Biotec, Mitsubishi Tanabe, MSD, Novartis, Prometheus, Roivant, Sanofi and Topadur. Patent issued "mir-29 for the treatment of systemic sclerosis" (US8247389, EP2331143) , Przemysław Błyszczuk: None declared, Gabriela Kania: None declared.